Dipole antenna system



June 13, 1950 E, Q, wlLLOUGHBY 2,511,029

DIPOLE ANTENNA SYSTEM Filed Feb. 18, 1946 INVENTOR Ek/C 0. W/LLOUGHBY *"I BY W ATTORNEY Patented June 13, 1950 UNITED STATES PATENT OFFICE DIPOLE ANTENNA SYSTEM Delaware Application February 18, 1946, Serial No. 648,507 In Great Britain February 6, 1945 Section 1, Public Law 690, August 8, 1946 Patent expires February 6, 1965 11 Claims.

The present invention relates to dipole antenna systems and has for its object to provide a very rigid type of dipole antenna suitable for use in cases where high mechanical strength is required, as for example, on aircraft. Another object of the invention is to provide a rigid type of band-pass dipole antenna suitable for use, for example, on aircraft or other cases where high mechanical strength is required.

According to one aspect of the present invention a dipole antenna system comprises two rigid conducting members each electrically unbalanced with respect to earth about a feed point located intermediate the ends of the respective members, said members being arranged insulated from each other to overlap at least along a portion of the lengths thereof so that the system is electrically balanced with respect to earth about an intermediate point and a transmission line having one conductor connected to one member and the other conductor connected to the other of said members at said feed points.

According to another aspect of the invention a dipole antenna system for operation over a broad band of frequencies comprises two like conducting members each electrically unbalanced with respect to earth about respective intermediate feed points along the lengths thereof, said members being arranged to overlap along the entire lengths thereof but insulated from each other and the one reversed with respect to the other and means for short circuiting the adjacent ends of the members, the system being electrically balanced with respect to earth about the central transverse axis, and the short circuited slot transmission lines formed by oppositely disposed edges of said members being so designed as to be anti-resonant at the midband operating frequency and a transmission line having its conductors connected to respec tive ones of said members at said feed points.

Preferably, but not essentially, the dipole is mechanically symmetrical about the central transverse axis at which the feed line is connected and which is thus at the centre of the overlapping portions. The conducting members may be of any desired cross sectional shape and when the antennae are to be airborne as when used on aircraft they may very suitably and conveniently be made tubular in form having a stream line sectional contour.

Other features of the invention will be apparent both from the following description taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the invention, and from the appended claims.

In the drawings:

Figure 1a is a sectional plan View of an antenna embodying the invention.

Figure 1b is a transverse section taken along the line AA in Figure 1a. and looking in the direction of the arrows.

Figure 1c is a side view of the antenna shown in Figures la and 1b.

Figure 2a is a side view and Figure 2b is a plan view of another embodiment and Figure 2c is a transverse section along the lines B--B in Figures 2a and 2b.

Figure 3a. is a perspective view of another embodiment of the invention and Figures 3b and 3c are transverse sections along the lines C-C and D--D respectively of Figure 3a, and

Figure 4 is a side view of a further embodiment.

The antenna shown in Figures 1a, b and 0 com-- prises a hollow cylindrical member l of conducting material, for example of sheet metal formed into a tube of section shown in Figure 1b, and closed at its ends by suitably shaped end pieces. A Z-shaped slot 2 is cut; out of the sheet on the upper and lower sides and symmetrically disposed about a transverse central plane passing through the line 33. The limbs of the Z- shaped slot 2 need not go to extreme ends of the antenna but may terminate some distance from the ends as shown. There is thus formed two elements, one comprising the portion t and arm 5 and the other comprising the portion 6 and arm 1. The arm 1 overlaps the portion 4 and the arm 5 overlaps the portion 6. Portions c and I are connected together by end piece 8 and portions 5 and 6 are connected together by end piece 9. The element 4, 5 is connected to one conductor of a transmission line, for example the outer conductor It, and may be secured thereto and the element 6, l is connected to the other conductor, Or in the example given the inner conductor II, as shown in Figure 10,. Thus the two elements overlap at 4, 1 and 5, S and the portion 4, and end part 8 of element 4, 5 has a greater capacity to earth than the arm 5 on the opposite side of the transverse section 3-3 and likewise the portion 6 and end part, 9 has a greater capacity to earth than the arm 1, and hence the effective dipole is composed of the difference of capacities to earth of 4, 8 and 1 of the one element of the antenna and by the diiierence of capacities to earth of 6, 9 and 5 of the other element. It is equally true to say that the elements of the dipole antenna are effectively 3 formed by the net out of balance of the member 4, 5. 8 on the one hand about the feedpoint in plane 3-3 and on the other hand by the net out Of balance of the member 6, 1, 9 about 3-3.

Such a system as that Shown in Figs. la-c may be constructed from two tubular members which have equal portions cut away as will be clear.

The overlapping of the two elements at 4, and 5, 6 enable a rigid structure to be obtained.

To render the dipole thus formed for use over a broad band of frequencies, the slots between the portions 4 and 5 and the arms 6 and 1 respectively are so constructed that with their end capacity they form short circuited transmission lines anti-resonant at the midband operating frequency.

In Figures 2a, 2b and 2c is illustrated another embodiment somewhat similar to that shown in Figures lac and its construction can best be seen from Figure 2b and the section shown in Figure 2c. The antenna comprises a tubular member l2 having at its central transverse plane two arcuated slots l3, M which divide the member |2 into two portions l5 and I6 united by portions l8, one on each end of a diameter. Longitudinal slots I9, 20 on one surface are provided in the portion l5 and slots 2|, 22 are provided in the diametrically opposite surface of portion l6. Thus a tongue 23 may be looked upon as a continuation of [6 and tongue 24 a continuation of portion l5. The portion l5 and tongue 23 are connected together by the end portion 25 and likewise portion l6 and tongue 24 are connected together by the end portion 26. It will be observed that the member comprising portion l5 and tongue 24 is electrically unbalanced about the slots l3, l4 because the capacity to earth of I5 is greater than the capacity to earth of 24. Likewise the element comprising portion I5 and tongue 23 is electrically unbalanced about the slots l3 and M. It can be easily seen however that the arrangement as a whole is electrically balanced about the slots I3 and I4.

One of the feed line conductors is connected to one of the elements, for example, the outer conductor 2'! of a coaxial line is secured to the element comprising portion l5 and tongue 24. The other or inner conductor is connected to the tongue 23.

The portions 25 and 26 may take the form of end caps which connect together tongue 23 and portion I5 or tongue 24 and portion l6. For wide band operation the short circuited transmission lines formed by the edges of the slots |922 are together with their end capacity at the centre made anti-resonant at the midband operating frequency when seen from the feed line 21. The dipoles of the antenna are effectively formed by the net out of balance of member 25, 5, 24 about the feed point or central transverse plane and by the net out of balance of member 25, I6, 23 about said transverse plane.

In the construction shown in Figures 3a, 3b, and 3c the antenna comprises a cylindrical member having at its centre transverse plane 28 two arcuate slots 29, 30, and the portion on the left hand of the plane 28 has two longitudinal slots 3|, 32 forming a tongue 33 connected to the upper portion 4| on the right hand of the plane 28 at 34 between the arcuate slots. Likewise the portion of the cylindrical member on the right hand of the plane 28 has two longitudinal slots 35, 36 forming a tongue 31 connected to the lower portion 42 on the left hand of the plane 28 at 38 between the arcuate slots. The ends of the tubular member are closed by conducting discs 39, 40.

It will be observed that the antenna comprises two compound elements, namely the right hand upper portion 4| and tongue 33, and the left hand lower portion 42 and tongue 31.

The elements may therefore be made from sheet metal having similar portions cut away in one half to form the tongues 33, 3! respectively.

The outer conductor 43 of a coaxial line may be connected to the portion 42 and tongue 31 and the inner conductor to the portion 4| and tongue 33 and the dipoles are effectively formed by the net out of balance of 33 and 4| and 31 and 42 about plane 28.

As in the two preceding embodiments for wide band operation the short circuited slot transmission lines formed by the edges of slots 3|, 32, 35, 38 are made of such lengths as to be antiresonant at the midband operating frequencies. It will be observed that the element 4| and 33 is unbalanced about the plane 28, as is also the element 31, 42, but that the system as a whole is balanced about the plane 28 which substantially contains the feed point.

It will be observed that there are connected in parallel across the transmission line the effective dipole and the slot transmission lines short circuited at one end.

To increase the operating frequency band width the characteristic impedance of the short circuited transmission lines formed by the slots 5, 6; 4, 1 (Fig. 1) 20, 22 (Fig. 2), 3|, 32, 35, 36, (Fig. 3) is so arranged that the reactance changes on moving ofi resonance at a frequency are substantially equal and opposite to the changes of the effective series resonant circuit formed by the equivalent overall dipole across the transmission feeder line throughout a range of frequencies on either side of the resonant frequency. This can be done by varyin the widths of the transmission line slots or their lengths.

If the short circuited slot transmission lines are less than one quarter wavelength at the mid band operating frequency, a satisfactory frequency band can still be obtainable by parallel tuning to anti-resonance by means of a shunt capacity 44, illustrated diagrammatically in Figure 4 as a parallel plate condenser having one plate fixed and the other adjustable by means indicated at 45 as a rod which may project outside the aerial for manipulation. Otherwise the antenna in Figure 4 is the same as that shown in Figure 1 or 2. Alternatively the short circuited slot transmission lines may be shortened by filling the tubular members and slots with polythene or other suitable dielectric material to reduce the resonant length as indicated by the shading in Figure la.

What is claimed is:

1. A dipole antenna system comprising two rigid conducting members each electrically unbalanced with respect to earth about a feed point located intermediate the ends of the respective members, said members being arranged insulated from each other to overlap along the whole lengths thereof with the adjacent ends thereof electrically short circuited so that the system is electrically balanced with respect to earth about an intermediate point, and a transmission feeder line having its conductors connected to respective ones of said members at said feed points.

2. A dipole antenna system comprising two rigid like conductor members each electrically unbalanced with respect to earth about an intermediate feed point along the length thereof, said members being arranged the reverse of the one with respect to the other and insulated one from the other to overlap along their entire lengths with the adjacent ends of the members short circuited so that the system is electrically balanced with respect to earth about said intermediate point and a transmission line having its conductors connected to respective ones of said members at said intermediate feed points.

3. A dipole antenna system for operation over a broad band of frequencies comprising two like conducting members each electrically resonant at the midband operating frequency and electrically unbalanced with respect to earth about respective intermediate feed points along the lengths thereof, said members being arranged to overlap along the entire lengths thereof, but insulated the one from the other and the one reversed with respect to the other, and means for short circuiting the adjacent ends of the members, the system being electrically balanced with respect to earth about the central transverse axis, the oppositely disposed edges of said members and the means short-circuiting the ends thereof forming short circuited slot transmission lines so designed as to be anti-resonant at the midband operating frequency and a transmission line having its conductors connected to respective ones of said members at said intermediate feed points.

4. A dipole antenna for operation over a broad band of frequencies comprising two like conducting members each electrically unbalanced with respect to earth about respective intermediate feed points along the lengths thereof, said members being arranged to overlap along the entire lengths thereof, the one reversed with respect to the other, means for short circuiting the adjacent ends of the members, the system being electrically balanced with respect to earth about the central transverse axis, and a transmission line having its conductors connected to respective ones of said members substantially at said intermediate feed points, the oppositely disposed edges of said members and the means short-circuiting the ends thereof forming short-circuited slot transmission lines so designed that the reactance changes of the characteristic impedances of the lines at frequencies differing from the resonance frequency are substantially equal and opposite to the changes of the effective series resonant circuit formed by the equivalent overall dipole across the transmission line.

5. A dipole antenna system as claimed in claim 4, said two overlapping members short circuited at the adjacent ends thereof comprising a conducting tubular member having continuous longitudinal slots in the wall thereof for a portion of the length and located in longitudinal planes on opposite sides of the medial plane and symmetrical about the transverse axial plane and arcuate slots connecting the longitudinal slots on opposite sides of said medial and transverse axial planes.

6. A dipole antenna system as claimed in claim 4, said two overlapping members short circuited at the adjacent ends thereof comprising a conducting tubular member having in one half of its length a longitudinal slot therethrough on one side of a medial plane and in the other half of its length a longitudinal slot therethrough on the other side of said medial plane and an arcuate slot in the transverse axial plane connecting the slots on opposite sides of said medial plane, and conducting means for closing the ends of said tubular member.

7. A dipole antenna system as claimed in claim 4, said two overlapping members comprising two like conducting sheets, having portions cut away on one side of the transverse axis, the two sheets being arranged the one reversed with respect to the other to overlap and curved in opposite directions above a longitudinal axis to form a tubular member having two longitudinal Z-shaped slots and conducting means for closing the ends of said tubular member.

8. A dipole antenna system as claimed in claim 4, said two overlapping members comprising a tubular conducting member having substantially at its central transverse plane two equal arcuate slots, the portion of said tubular member on one side of said transverse plane having two longitudinal slots forming a tongue connected to the portion of said tubular member on the other side of said transverse plane between one pair of ends of said arcuate slots and the other portion of the tube on the other side of said transverse plane having two longitudinal slots forming a tongue connected to the other portion of said tubular member on said one side between the other pair of ends of said arcuate slots.

9. A dipole antenna for operation over a broad band of frequencies comprising a conducting tubular member provided in one half of its length with a longitudinal slot therethrough on one side of a medial plane and in the other half of its length with a longitudinal slot therethrough on the other side of said medial plane and in the transverse axial plane with an arcuate slot therethrough connecting said longitudinal slots, conducting means closing the ends of said member, and a transmission line having one of its conductors connected to said tubular member at one side of said arcuate slot and its other conductor connected to said tubular member at the other side of said arcuate slot at a point diametrically opposite the point of connection of said one conductor, said longitudinal slots and said short circuiting means forming short-circuited transmission lines designed to be anti-resonant at the midband operating frequency.

10. The dipole antenna systems as claimed in claim 9, said member being so designed as to be half wave resonant at the midband operating frequency.

11. The dipole antenna systems as claimed in claim 9 wherein the said member is filled with polythene or other dielectric material.

ERIC OSBORNE WILLOUGHBY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,299,218 Fener Oct. 20, 1942 2,345,735 Douma Apr. 4, 1944 2,414,266 Lindenblad Jan. 14, 1947 FOREIGN PATENTS Number Country Date 877,658 France Dec. 14, 1943 

